1. Field of the Invention
The present invention relates to a control device for controlling various loads in a copier or the like, such as light source or heat source.
2. Description of the Prior Art
In the field of copiers and the like there is already known a method for controlling for example the amount of light from a light source, by comparing the voltage supplied to the light source with a reference voltage and controlling the power to be supplied to said light source according to a signal obtained from said comparison.
Such control method, if conducted in analog form, is unable to rapidly responding to the noises from other devices in the apparatus, thus often giving rise to erroneous control. Such erroneous control is undesirable particularly in a copier utilizing a photosensitive member, since even a slight change in the amount of light from the light source will significantly affect the image contrast.
Also in such control method, the power supply to the loads such as the light source is generally initiated at the start of power supply to the apparatus or in response to an instruction for starting the copying operation. In such case, the amount of power supply to said loads is usually same as in the normal copying operation. However, an initial power supply to the light source same as in the normal operation may lead to damages in the elements such as transistors and triacs for light control because of a surge current.
Also in case of controlling a load such as the light source by an AC power source, the sinusoidal waveform at the positive side is not completely symmetrical with that at the negative side. Consequently a phase control for the sinusoidal waveform of the positive side based on the obtained from the sinusoidal waveform of the negative side may lead to an error in the control, thus making satisfactory power supply impossible.